Cloud Concepts
AZ-900 begins with the vocabulary of cloud computing: why organizations adopt the cloud, how costs shift, and the service and deployment models. Mastering these concepts frames every other Azure topic.
Benefits of cloud computing
The cloud offers high availability, scalability, elasticity, reliability, and global reach without owning hardware. Scalability adds capacity as planned, while elasticity adds and removes it automatically in response to demand. Fault tolerance and disaster recovery improve reliability by tolerating component failures and recovering from outages.
CapEx versus OpEx
On-premises infrastructure is a capital expense (CapEx): large upfront purchases you depreciate. The cloud shifts spending to an operating expense (OpEx): pay-as-you-go consumption billed for what you use. The consumption-based model means you pay only for resources consumed and can stop paying by deprovisioning them.
Shared responsibility model
Responsibility for security and operations is divided between Microsoft and the customer and shifts by service model. Microsoft always secures the physical datacenter, network, and hosts; the customer always manages its data, accounts, and access. Responsibility for the operating system and applications depends on whether you use IaaS, PaaS, or SaaS.
Service models: IaaS, PaaS, SaaS
Infrastructure as a Service provides virtual machines and networking that you manage down to the OS. Platform as a Service provides a managed environment for building and deploying apps without managing the OS. Software as a Service delivers finished applications like Microsoft 365 that you simply use.
Deployment models
A public cloud runs on shared Microsoft infrastructure. A private cloud is dedicated to one organization, on-premises or hosted. A hybrid cloud connects public and private so workloads and data can move between them, useful for gradual migration or keeping some data on-premises.